1. Field of the Invention
The present invention relates to a stop-end pipe for creation of the joining surfaces between underground wall elements formed by casting concrete in situ.
2. Description of the Prior Art
This technique, which has been known for some years now, involves the following steps:
performing an excavation in the form of a trench, always in the presence of bentonite slurry, using various tools, including special buckets having a width and a length which are substantially the same as, or a submultiple of, the width and length of the excavation, the width as well as the depth of the excavation corresponding respectively to the width and the depth of the finished underground wall; PA1 immersing in the excavation, still full of bentonite slurry, a metal reinforcement for the underground wall, if required; PA1 filling the excavation with concrete, starting from the bottom, the bentonite slurry floating on the concrete and being expelled upwards as the level of the latter gradually rises from the bottom; and PA1 leaving the concrete thus cast in the first excavation to set and carrying out the operations again, from the beginning, for a second excavation arranged next to and in line with the first excavation. PA1 on the one hand, owing to the fact that the deformable stop-end pipe consists of at least one double-wing profiled section which, during casting of the concrete, has a sufficiently rigid structure; and PA1 on the other hand, owing to the fact that, after hardening of the concrete casting and the action of a cleaning tool guided along a guide-channel formed in the profiled section, the profiled section itself can be easily deformed in a resilient manner and made to close up on itself by the movement, towards each other, of said wings about a resilient hinge.
Precisely this latter step in the process is particularly delicate since, along the surface of the vertical head side of the wall set in the first excavation, it is extremely difficult to form a perfect joint with the wall cast in the second excavation which does not give rise to problems either of a structural nature or associated with infiltrations.
Various techniques have been proposed in order to solve this problem; the invention relates in particular to those techniques, more recent, whereby, once a first excavation has been carried out, before performing casting of concrete therein, a so-called "stop-end pipe" or formwork with a special cross-sectional shape is inserted therein, said "stop-end pipe" or formwork being arranged vertically in the excavation so as to print, in the head surface of the wall cast in the first excavation, a shaped surface impression intended to facilitate subsequently joining with the wall which will be cast in the second excavation.
A first embodiment of the stop-end pipe has been known since 1977, according to which simple tubular elements having circular cross section were stacked one over the other inside the excavation.
However, upon the cast being performed, the concrete spills out onto the lateral sides of the circular tubular elements giving rise to the undesirable formation of concrete rings which encircles the surfaces of the formwork, further hindering removal thereof.
In the following years, this kind of circular pipe was dismissed and a new stop-end pipe was disclosed, in which the cross section of the tube was so shaped as to facilitate braking of concrete rings at predetermined positions, with great advantage for performing the next adjacent excavation. Further, in the shaped stop-end pipes, the side facing the concrete cast is formed in such a way as to print, in the head surface of the wall cast in the excavation, an impression intended to facilitate subsequently joining with the wall which will be cast in the adjacent excavation.
However, the extraction operation of both types of stop-end pipes from the excavation still proves to be fairly difficult and must be performed before the concrete has set fully--for example within three or four hours of casting--with the risk of at least part of the concrete collapsing.
In order to overcome this difficulty, solutions have been proposed in which the formwork is extracted by exerting a pulling force in the horizontal direction, obviously after the second excavation has been performed.
More precisely, there is known a formwork which has an essentially trapezoidal cross-sectional shape, and having guiding elements apt to guide an extracting tool. The main drawback of this arrangement consists in the fact that the formwork despite also has a trapezoidal shape intended to facilitate extraction, in practice remains attached to the casting of the side of the first excavation with a resistance which increases the longer the concrete is allowed to set. In order to overcome this adhesive resistance, it is therefore necessary to use a very heavy and efficient hammering tool, said tool being able to apply to the formwork impacts directed towards the head of the wall and respectively in the opposite direction, precisely in order to cause separation of the formwork. It can be easily understood that this arrangement requires a complex way of working and that a formwork which is subject to this treatment has only a very short working life.